1. Field of the Invention
The present invention relates to an image processing apparatus which efficiently reduces the amount of data, an image processing method, and a computer program.
2. Description of the Related Art
Conventionally, printing an image while changing the resolution for each pixel according to the characteristics of the image can prevent the generation of excessive data while maintaining the image quality, thus preventing deterioration in image quality and an increase in the amount of print data more than necessary.
Japanese Patent Application Laid-Open No. 9-220830 divides an image into a plurality of blocks having a predetermined size and determines whether each of the blocks has a uniform color. When a block has a uniform color, it is recognized as a low-resolution pixel. In this case, the block composed of several dots is practically used as one pixel. Otherwise, when the block does not have a uniform color, the block is recognized as a high-resolution pixel. In this case, print data having a plurality of resolutions is generated. A resolution changeover code is used to change between the low-resolution pixel and the high-resolution pixels.
In the above-mentioned method, since an image is divided into a plurality of blocks having a predetermined size and it is determined whether these blocks have a uniform color, the amount of data may not easily be reduced depending on the characteristics of the image even when many pixels of an identical value continue. For example, since an edge of text and graphics, a copy-forgery-inhibited pattern, and a lattice pattern do not have a uniform color, they are recognized as high-resolution pixels and therefore the amount of data cannot easily be reduced. FIG. 9 illustrates an exemplary lattice pattern image 901. When the image 901 is divided into six 4×4 blocks, blocks 902 to 907 are formed. Since the blocks 902 and 903 have a uniform color, they can be recognized as a low-resolution pixel as illustrated by an image 908. Since the blocks 904 to 907 do not have a uniform color, they are recognized as high-resolution pixels and therefore the amount of data cannot easily be reduced.
Further, when an exemplary image 909 representing an edge portion of graphics is divided into four 4×4 blocks, blocks 910 to 913 are formed. Since the blocks 910 to 913 do not have a uniform color, they are recognized as high-resolution pixels and therefore the amount of data cannot easily be reduced.